<sect1 id="ai-meridian">
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<author><firstname>Jason</firstname> <surname>Harris</surname> </author>
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<title>The Local Meridian</title>
<indexterm><primary>Local Meridian</primary>
<seealso>Hour Angle</seealso> <seealso>Celestial Sphere</seealso> </indexterm>
<para>The Local Meridian is an imaginary <link linkend="ai-greatcircle">Great Circle</link> on the <link linkend="ai-csphere">Celestial Sphere</link> that is perpendicular to the local <link linkend="ai-horizon">Horizon</link>. It passes through the North point on the Horizon, through the <link linkend="ai-cpoles">Celestial Pole</link>, up to the <link linkend="ai-zenith">Zenith</link>, and through the South point on the Horizon. </para><para>Because it is fixed to the local Horizon, stars will appear to drift past the Local Meridian as the Earth spins. You can use an object's <link linkend="equatorial">Right Ascension</link> and the <link linkend="ai-sidereal">Local Sidereal Time</link> to determine when it will cross your Local Meridian (see <link linkend="ai-hourangle">Hour Angle</link>). </para>
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